Most Pythonic way to store (small) configuration

Steven D'Aprano steve at pearwood.info
Wed Aug 5 16:08:13 CEST 2015


On Wed, 5 Aug 2015 11:46 pm, Rustom Mody wrote:

> On Sunday, August 2, 2015 at 3:44:51 PM UTC+5:30, Cecil Westerhof wrote:
>> There are a lot of ways to store configuration information:
>> - conf file
>> - xml file
>> - database
>> - json file
>> - and possible a lot of other ways
> 
> One that I dont think has been mentioned:
> ast.literal_eval


Probably because it doesn't work :-)

py> import ast
py> s = "x = 23"  # pretend I read this line from a file
py> ast.literal_eval(s)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.3/ast.py", line 47, in literal_eval
    node_or_string = parse(node_or_string, mode='eval')
  File "/usr/local/lib/python3.3/ast.py", line 35, in parse
    return compile(source, filename, mode, PyCF_ONLY_AST)
  File "<unknown>", line 1
    x = 23
      ^
SyntaxError: invalid syntax


You might be able to build Yet Another Config Format using literal_eval as a
building block, for evaluating values, but *in and of itself* it isn't a
way to store config information, any more than

int
float

or any other function which takes a string and evaluates it as a Python
primitive or built-in type.


However, there are at least config formats in the standard library which I
believe we've missed: shelve, and plistlib.

help(shelve)

    A "shelf" is a persistent, dictionary-like object.  The difference
    with dbm databases is that the values (not the keys!) in a shelf can
    be essentially arbitrary Python objects -- anything that the "pickle"
    module can handle.  This includes most class instances, recursive data
    types, and objects containing lots of shared sub-objects.  The keys
    are ordinary strings.


help(plistlib)

    The property list (.plist) file format is a simple XML pickle supporting
    basic object types, like dictionaries, lists, numbers and strings.
    Usually the top level object is a dictionary.


-- 
Steven



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